Biofouling in industrial waters, which occurs as a result of the presence of microorganisms, is a significant concern for industrial manufacturers. Industrial processes subject to problems with biofouling include those used for the manufacture of pulp, paper, paperboard, and textiles, particularly water-laid nonwoven textiles. Other examples of industrial waters where microorganisms can interfere with industrial processes include cooling tower waters, minting process waters, food processing waters, sugar reprocessing waters, and wine or brewery waters. For example, in the manufacture of paper, paper machines handle very large volumes of water in recirculating systems called "white water systems." The furnish to a paper machine typically contains only about 0.1-2% of fibrous and nonfibrous papermaking solids, which means that for each ton of paper a very large amount of water passes through the headbox of which most is recirculated in the white water system.
The presence of microorganisms within industrial water systems results in the formation of deposits of biological origin on industrial machines. These formation deposits give rise to: corrosion, breaks, increased down time, loss of yield, high chemical costs, odors, and expensive deposit control programs. In the paper mill industry, slime deposits are reportedly responsible for nearly 70% of all breaks, blockages and pump failures. Safade, Tackling the Slime Problem in a Paper-Mill. PTI, p. 280 (September 1988). Slime may be defined as an "accretion or accumulation caused by certain microorganisms in the presence of pulp fiber, filler, dirt and other materials, mixed in varied proportions, having variable physical characteristics and accumulating at continuous changing rates." Id. An excellent growth media for microorganisms is provided because of the warm temperatures and rich carbohydrate containing fluids of paper machines which provide ideal growth conditions. The contaminating microorganisms are capable of causing spoilage of pulp, furnish, or chemical additives, because of the build-up of slime masses in headboxes, waterlines and papermaking equipment. When deposits break loose and fall into the paper furnish, they result in quality loss or end product defects such as holes and spots. Bad odors in the paper and web breaks which can cause costly disruptions in paper machine operations are among the other detrimental effects of microbial growth. The end result is unsalable paper or paper sold at a lower value. Robertson, The Use of Phase-Contrast Microscopy to Assess and Differentiate the Microbial Population of a Paper Mill. TAPPI Journal, p. 83 (March 1993).
The conventional method of controlling microbial growth is through the use of biocides. Biocides are generally divided into two main groups: oxidizing; and non-oxidizing. These biocides act on the microorganisms in one of three ways: either by attacking the cell wall, the cytoplasmic membrane, or the cellular constituents. Id. at 282.
To control biological fouling, it is common in the art to treat the affected water systems with certain chemical substances in concentrations sufficient to kill or greatly inhibit the growth of the causative organisms. For example, chlorine gas and hypochlorite solutions made with the gas have long been added to water systems, to kill or inhibit the growth of bacteria, fungi, algae, and other troublesome organisms. However, chlorine compounds are not only damaging to materials of construction, but they also react with organics to form undesirable substances in effluent streams, such as carcinogenic chloromethanes and chlorinated dioxins.
Certain organic compounds, such as methylenebis(thiocyanate), dithiocarbamates, haloorganics, and quaternary ammonium surfactants, have also been used. While many of these are quite efficient in killing microorganisms or inhibiting their growth, they also tend to be toxic or harmful to humans, animals, or other non-target organisms; as well as expensive.
Glutaraldehyde in combination with various other biocides is described in U.S. Pat. Nos. 5,368,749, 5,198,453, and 5,209,824 for the controlling of microorganisms found in industrial process waters.
As an alternative to treatment with biocides, researchers posited the use of enzymes to control slime accumulation. U.S. Pat. No. 3,824,184 to Herbert J. Hatcher describes to the addition of levan hydrolase to industrial waters having a slime accumulation or potential slime problem. Similar to using a mixture of various biocides, the use of a multiple enzyme blend to control industrial slime is also known. See U.S. Pat. No. 5,071,765 to Christopher L. Wiatr. However, field trials indicate that these enzymatic treatments are ineffective in papermaking applications.
While a biocide or an enzyme alone inhibits slime growth, researchers report that the combination of a biocide and an enzyme together provides even greater benefits. For example, U.S. Pat. No. 4,684,469 to Pederson et al. discloses to the combination of a biocide and a polysaccharide-degrading enzyme to reduce slime accumulations. However, though the combination of the biocide and the levan hydrolase may provide increased control against some sorts of slime growth, it has no effect on sheathed microorganisms.
Combinations other than that of biocide and enzyme have also found utility in the prevention of microbiological fouling. Surfactants, such as ethylene oxide/propylene oxide (EO/PO) copolymers have been utilized in conjunction with biocides to control slime formation in the papermaking industry. U.S. Pat. No. 5,128,133 to Hidaka et al. discloses the use of the non-oxidizing biocides 4,5-dichloro-1,2-dithiol-3-one and N-dodecyl guanidine hydrochloride or N-dodecyl guanidine acetate, and recommends the concurrent addition of a surfactant such as an ethylene oxide/propylene oxide copolymer. U.S. Pat. No. 4,770,790, to Oberhofer discloses a process for improving performance of water treatment solids which can be fouled with micro-organisms by treatment with a biocide, a nonionic surfactant and a biodispersant. Oxidative biocides used in conjunction with ethylene oxide/propylene oxide adducts are described therein, yet only halogenated oxidative biocides are disclosed. Further, U.S. Pat. No. 4,295,932 to Pocius discloses a method for controlling aqueous systems heavily contaminated with microorganisms comprising treating the system with a non-oxidizing halogenated biocides and a biodispersant EO/PO copolymer.
Another difficulty with conventional treatments is that they often fail to recognize the problems caused by filamentous microorganisms in water systems. A group of microorganisms, including the filamentous bacteria, enter industrial systems via the fresh waters. In a typical treatment program, the proper chlorination of waters is always recommended as a means to kill these microorganisms before they enter the system. Unfortunately, proper chlorination is often not a viable option since many of the filamentous bacteria have, a protective sheath that shields them from antimicrobial agents. In fact, research has shown that 85% of the paper machine deposit samples for alkaline mills currently show filamentous bacteria as one of the major portions of the deposit matrix, despite conventional biocidal treatment. One solution to the problems presented by the presence of filamentous bacteria in industrial process waters is disclosed in U.S. Pat. Nos. 5,324,432 and 5,395,530. The method disclosed in these patents is the addition of an effective amount of an enzyme and a biocide to enhance the kill of filamentous microorganisms.
Nonetheless, a need exists for improved methods for controlling the growth of microorganisms in industrial process waters, including the filamentous microorganisms. A treatment such as the non-halogenated oxidative biocide in combination with a biodispersant that the Applicants disclose herein is desirable because of its low cost, decreased toxicity to the environment, and activity against a greater variety of microorganisms.